Paenungulata
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Paenungulata is a superorder that groups some remarkable mammals constituting three orders:
- Proboscidea (Elephants)
- Sirenia (Sea cows, including dugongs and manatees)
- Hyracoidea (Hyraxes, such as the African Rock Hyrax, Procavia habessinica)
All three still exist but the Paenungulata once had at least two additional orders, namely:
Both of these were as unique in their ways as the surviving orders. Embrithopods were rhino-like herbivorous mammals with plantigrade haid feet, and desmostylians were hippopotamus-like amphibious creatures resembling a hippopotamus, the walking posture diet of which has been the subject of speculation. However tooth wear indicates that Desmostylians browsed on terrestrial plants and had a similar posture to other large hooved mammals.
George Gaylord Simpson, (Simpson 1945), working with traditional taxonomic techniques did succeed in grouping these spectacularly diverse mammals in the superorder he named Paenungulata, but there were many loose threads in unravelling their genealogy. The Hyraxes in his Paenungulata ("almost ungulates") offered hints that they might be connected to the perissodactyl ungulates— horses and rhinos and kin. Indeed early taxonomists placed the Hyracoidea as closest to the rhinoceroses, because of their dentition, and some evidence possibly suggests an affinity of Hyracoidea to Perissodactyla, rather than to the rest of the Paenungulata. If this is so, then Paenungulata are not most closely related to one another.
Then genetic techniques were developed of inspecting the differences among amino acid differences among hemoglobin sequences. The most parsimonious cladograms depicted Simpson's Paenungulata as an authentic clade and as one of the most anciently diversified among the placental mammals (Eutheria), that is, among the first group to diversify from the basal placental mammals. The hypothetical connections with Perissodactyls were not supported by the amino acid sequences, although morphology continues to support the position of Paenungulates as Ungulates.
The molecular evidence suggests that Paenungulata in its turn is part of Afrotheria, an ancient assemblage of mainly African mammals of great diversity. The other members of this superorder are Afrosoricidans (tenrecs and golden moles), elephant shrews (Macroscelidea) and aardvarks (Tubulidentata).
Of the orders of Paenungulates mentioned above, hyraxes are the most basal, followed by embrithopods, sirenians and desmostylians, with elephants being the crown group. The latter three are grouped as the Thetytheria.
[edit] References
- Simpson, G. G., "Classification," in Bulletin of the American Museum of Natural History vol. 85:1-350. 1945.
- McKenna, M. C. and Bell, S. K., editors, Classification of mammals; above the species level. Columbia University Press, New York, 1997.
